Tig welding tips, questions, equipment, applications, instructions, techniques, tig welding machines, troubleshooting tig welding process
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Here's my Friday project... A new vacuum penetration in a liquid oxygen trailer. The old had cracked, through the inner pipe, allowing air and LOX to get into the vacuum jacket. The fun part was coping a piece of 6" sch.40 to the radius of the rear head.
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Naw... the fun part was standing on my head to weld the bottom of this...

Steve S
racingparts
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i weld aluminum almost every day
here are some 1.5mm thick radiator headers

i want to start welding SS, will buy some pipes to make an exhaust for my racing bike

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Here we go, again.

I'll weld this mess tomorrow. One of these visible cracks is leaking! (The topmost right.) I'll spend the afternoon grinding this out.
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Alexa
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Otto Nobedder wrote:Here we go, again.

I'll weld this mess tomorrow. One of these visible cracks is leaking! (The topmost right.) I'll spend the afternoon grinding this out.
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Otto Nobedder.

From the photo, it invites me to think that a section of the plate, that had been welded in a tee-joint, was cut out.
Was the welded tee-joint The part cut out seems to had also been welded. What was the original bevel configuration of the tee-joint? Full penetration? Welded from both sides? Base material? In short ... how had it been welded?

The red indications from the dye penetrant testing seem to coincide with the locations of the tee-joint weld, but also with the grinding that was used to remove the remaining weld after cutting out the plate.

Keep us informed as to what type of crack and if possible, what path it took through the base metal.
I am curious to find out if other cracks will be discovered.

Tanks.
Alexa
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Alexa,

Here's a better pic to answer a part of your question:
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The section removed is 1/4 X 3", 304 flatbar rolled to a 24" radius. Fillet weld, both sides, no bevel.

As you surmised, the cracks are between the (MIG) fillets, generally perpendicular to the tangent of the "ring".

This is not the first time I've encountered this on this design. My suspicion is these vessel heads (also 304 SS) were cold-formed without annealing, inducing natural stresses. The fillet welds add stresses of their own. The purpose of the ring is to distribute forces from the sole "front-to-back" support for the inner vessel, meaning the entire weight of the inner vessel and it's cargo are pushing and pulling on this structure every time the driver hits the throttle or brake.

I see it as a design flaw, that has taken about 25 years to rear it's ugly head, and I expect to see more like this in the near future as all the trailers in this design series are near the same age.

Steve S
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Here's the evidence proving the leak... At 1 PSIG pressure in the annular space!
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Here's what it took to eliminate the cracking... The head is nearly 1/2" thick (formed originally from 1/2" 304 sheet). Note the one that leaked was ground through completely. There's an 18 ga. "backing strip" inserted and held firmly in that one.
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Steve S.
Alexa
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Otto Nobedder.

If the cold working during the forming of 304 plate is great enough, this increases the probability of stress corrosion cracking. It seems like the equipment operates with repetitive stresses. The equipment might have an corrosive environment internally (example: chlorinated water, or salt water.).

If the cracking occurred only at the location of the welds or very close to the welds, then it invites to think that during the welding of the fillets, the microstructure might of been made even more susceptible to stress corrosion cracking.

So we have accumulated risks possibly from:
- the choice of 304 instead of 304L (L = low carbon)
- the cold working during forming without annealing
- the heat input during welding may of been excessive
- the stresses during the operation of the equipment
- the corrosive fluids (if any) circulating within the equipment during its operations

I am curious to know if the metal located under and next to the rest the welds has cracks also, even if the cracks may have not yet 'grown' to reach through-wall thickness lengths.

What is the fluid that circulates internally?
How hot does the equipment reach during operation?

Tanks.
Alexa
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Excellent questions!

There is NO working fluid behind this metal; It is evacuated equivalent to deep space.

These are like huge Thermos bottles... An inner vessel full of coffee, an outer vessel with a handle, and vacuum in the middle.

It's a bit more complicated than that... There are many layers of Mylar/tissue as a radiant barrier, as well.

Short form, the "backside" of those cracks sees nothing but extreme vacuuum. That's the leak-detection method; Helium mass-spectrometry. The front side of these cracks haven't seen the light of day since the trailer was built.

The cracking always seems to begin directly between the fillet welds, but has extended to just beyond the weld zone. (Loss of vacuum and inherent loss of insulation bring these problems to our attention before they could progress farther, so how far they COULD extend over time is open to speculation.

Steve S
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Also, in answer to another of your questions,

Of the five cracks visible in the photo with the dye-penetrant, only one was leaking. There could be many smaller cracks around the structure that have simply not shown themselves through leakage yet.

Steve S
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In answer to your last question, the outer vessel in the pictures reacts solely to ambient temperature. 110 degrees in the sun in July, 22 below in Iowa in the winter.

The inner vessel operates at -423*F, but with minimal influence on the outer.

Steve S
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Not sure on the diameter but its something like 9' round....flange was cut back and we are re welding inside and out. 1/4 rolled gores and a 3 x 3 3/8 angle flange...good times out in the potash mines in Saskatchewan!
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Mrkil
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I've been working on this in school for a bit. My wife collects old tin robots, so I wanted to make he one cor her birthday.
It is finished. I'm going to work on some patina methods to give it some "age"

It's all 1/16 sheet with the exception of the feet and arms that are 1/8.

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Hey,

That is very cool. Your wife will love it, simply because of the effort you put into it. And because its awesome .

Have you checked out www.browndogwelding.com ? He makes robot sculptures and they rock.

Mick
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Why not "color case-harden" it?

That'd be a cool finish for a retro robot!

Steve S
Mrkil
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Interesting. I'll have to look into that.
blaz
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Had to make a new mount for this motor. New location means lots of mods. Machined the flange mount plate and slotted the angle iron in order to tension the chain.

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Welds are looking OK. I think I needed to add more filler on the angle iron.
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Blaz,

I think you're golden with that amount of filler and tie-in.

I also noted you have a sense of safety... I saw where you marked "hot"...

Not everyone thinks of that.

Steve S
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Thanks for the comment Steve. Like everyone, I am still learning. Every little bit of info goes in the memory bank.

I won't mark it hot on the welding bench. If it leaves the welding area, it gets marked HOT! It only takes a second. :D

I enjoy TIG welding, so it is time to get one for home. I have a syncrowave 250dx @ work and it is great but I can't afford one for home. I am currently looking @ a lincoln squarewave 175. I did look at the diversion 180 but I like the stick option on the lincoln. Is it worth the extra $700 to get an inverter machine when all I have ever used is a transformer machine? Yes, I should ask this elsewhere. :oops:
TamJeff
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Busted transom engine bracket that holds twin 250hp. It had previously been welded. 3/8" aluminum mounting plate with adjoining sides of 1/4". Analysis reveals that when they sanded the weld bead smooth, they took too much meat from a minimal weld to start with. I clamped a piece of 2"x2" angle aluminum to a standard 7-1/4" circular saw base with a carbide combination blade and cut the 1/4" side (top) back 5/16", creating a substantial open corner all the way across the top, exposing all but a 16th of the edge of the 3/8" plate.
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3 full penetration build passes, sanded flush and (the large plate was stretched) straight with a 3/16" bevel, and a finish cap bead on top in the event they decide to sand it smooth again, that there will be enough filler to save from compromising the weld, or having to make such a large radius round over to get to solid metal. Being that the joint came out nice, and is mostly obscured by both engines, I would leave the weld and just paint it if it were mine.

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I preheated the first 12" of the joint with a propane torch until I got it moving.
Miller ABP 330, Syncrowave 250, Dynasty 300 DX.
Honorary member of the Fraternity of Faded Tee Shirts.
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Again, something a bit different from me.
We do some fabrication work for a specialist gearbox and component company that builds high performance and racing gearboxes.
The pics below are part of the shifter arrangement we have to fabricate for our customer and these locate the shifter as it comes through the underfloor of the car to position the shifter in the correct position.
These are for for Rally cars and are full sequential dog gear gearboxes.
They are quite tricky to build as all the tubing is bent and cut and ground to shape by hand and as much welding as possible is done in the jig before removal when the welding is finished.
The tubing is all 4130 Cr/Mo and is small diameter 5/8" X .058", 1/2" X .065" and 3/8" X .058" tubing
Regards Andrew from Oz.

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We are Tig welders, gravity doesn't worry us.
Miller Dynasty 350
OTC hybrid wave 300 amp inverter Tig at work (Now retired)
Kemppi MLS 2300 inverter, 230 amps of welding brilliance for home use
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blaz wrote:Thanks for the comment Steve. Like everyone, I am still learning. Every little bit of info goes in the memory bank.

I won't mark it hot on the welding bench. If it leaves the welding area, it gets marked HOT! It only takes a second. :D

I enjoy TIG welding, so it is time to get one for home. I have a syncrowave 250dx @ work and it is great but I can't afford one for home. I am currently looking @ a lincoln squarewave 175. I did look at the diversion 180 but I like the stick option on the lincoln. Is it worth the extra $700 to get an inverter machine when all I have ever used is a transformer machine? Yes, I should ask this elsewhere. :oops:
In my opinion, there are two advantages to the inverter which may or may not apply to you. They are far lighter for a comparable capacity, and they offer more precision when welding aluminum, particularly thin sections.

The chief disadvantages are initial cost, more electronics vulnerable to failure, and potentially higher repair costs.

It might be worth looking at the Everlast 250 EX... Great price point for the features, and it has a 5 year warranty and an excellent track record for customer service, even better than the Red and Blue guys! Jody has a video or two reviewing it, and there's a recent topic here discussing it.

Here's the topic:

http://forum.weldingtipsandtricks.com/v ... f=2&t=2931

Steve S
blaz
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Everlast and thermal arc have crossed my mind a few times. I have had good luck with Lincoln and Miller thus far. Time to just pull the trigger. :lol:


I like the gear box braces! Looks like a lot of work.
Mrkil
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I have the Thermalarc 181i and have not been happy with the tig torch that comes with it.
When I first set it up i had trouble getting enough argon, causing a kind of sparkler action. It seems with the diffuser supplied would not let the end cap seal. Switching to a weldcraft diffuser sorted that out.

The other issues where that the tungsten when assembled was off centre (this was most obvious doing 1/8" open root work with a number 4 cup. It almost touched the side of the cup itself. Also the hand grip twists on the torch. Unfortunately this is a bit of a pain on 5g pipe for me because as I walk the cup the body starts turning causeing my wrist to start changing angles.

The nice thing is he lws where I got it has warrentied the torch. Hopefully the replacment is better.
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Welded this today:

Here's my buddy welding up the outer vessel we spent 6 hours fitting up (after removing for a repair to the inner vessel).
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And here's my project, the inner vessel supports at the nose of the same project:
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Here's a closer look:
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Steve S
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And today, I welded this... (same trailer)
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And I ran out of 1/8" ER70S-2... so used two 3/32 for half the root and the entire cap.
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It surprised me when I did the math. Two passes on that comes out to 10'-6" of weld. It was 3/16 carbon with a 1/8" backing bar, gap varying from 1/8" up to 3/8" from someone's sloppy cut & grind.

Had about five hours in it. Syncrowave 250DX set to 200A, and near full to full pedal the whole way. Had to stop and put the fan on it several times.

Steve S
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